Charging a trolling motor while running it

[rebocc]

Re: Charging a trolling motor while running it

Dang it, I wonder where the OP went? Maybe he is confused as to how we can look into our crystal ball and determine better than he what his needs are. Maybe he doesn't understand why we keep pushing a gas motor even after he has twice told us he is not interested in a gas motor. Maybe he took offense in us calling his thinking "ridiculous." It seems he is happy with his setup and would like to charge the batteries for weekend trips with a generator and charger and also use it to extend his run time while on the water if possible. Can we help him with that or is our knowledge limited to "get a gas motor?"

Thanks DWParker, I was on vacation.

There are indeed a lot of guys who seem determined to get me a gas boat motor, and i'm pretty much ignoring them. I think I'll go looking for electric boat forums, since what I'm doing doesn't really compute for a lot of guys.

Thanks all!

 

[Silvertip]

Re: Charging a trolling motor while running it

You can't really compare Amps at different voltages. A battery bank at 36 volts X 45 amps is similar to 120 volts X 15 amps.

I most certainly can since there are things going on that you are electing to ignore.
I'm giving you real world numbers sir. Your troller draws 46 amps at 36 volts. Period. You intend to replace the consumed current from that battery bank with a three bank charger powered by a 115 volt source (be it an extension cord or a generator). The charger that you intend to power has a maximum output of 5 amps per bank. If you are drawing 46 amps and only replacing 15 you are losing ground at 31 amps. It doesn't matter what the source capacity is -- the charger can only provide 5 amps per bank at 12.6 volts (or whatever the charger output voltage is).

Your estimate of generator power is also flawed. A 2KW unit is the AVAILABLE AC current of the generator. However, you are still stuck with a charger that only outputs 5 amps per battery. So it doesn't matter if you have a 500KW generator. As long as you stick with that small charger you will lose ground. Upgrade the charger to a 15 amp per bank and you have a workable system. That unit is the weak link your concept and that's all I'm trying to point out to you.

 

[dwparker99]

Re: Charging a trolling motor while running it

I most certainly can since there are things going on that you are electing to ignore.
I'm giving you real world numbers sir. Your troller draws 46 amps at 36 volts. Period. You intend to replace the consumed current from that battery bank with a three bank charger powered by a 115 volt source (be it an extension cord or a generator). The charger that you intend to power has a maximum output of 5 amps per bank. If you are drawing 46 amps and only replacing 15 you are losing ground at 31 amps. It doesn't matter what the source capacity is -- the charger can only provide 5 amps per bank at 12.6 volts (or whatever the charger output voltage is).

Your estimate of generator power is also flawed. A 2KW unit is the AVAILABLE AC current of the generator. However, you are still stuck with a charger that only outputs 5 amps per battery. So it doesn't matter if you have a 500KW generator. As long as you stick with that small charger you will lose ground. Upgrade the charger to a 15 amp per bank and you have a workable system. That unit is the weak link your concept and that's all I'm trying to point out to you.

Both Silvertip and the OP seem to be mixing apples with oranges. The OP is mixing AC and DC amps and Silvertip is mixing 12 output with 36 volt output. If you convert input and output to power/watts it will be easier to understand. The TM output at max thrust is 46 amps at 36 volts or 1656 watts. The charger input at max amps is 15 amps at 12 volts or 180 watts. The input would be less than 1/10 of the output. Even at 15 amps per bank input, the input would be less than 1/3 the output.

As I stated in an earlier post, understanding how the charger works is as critical as knowing the input versus output if you are going to charge while using the TM. If you charger is like mine and tests the battery when first plugged in and then shuts down for 24 hours if they are 100%, you could run the generator all day and may never put anything back into the system.

 

[duke33]

Re: Charging a trolling motor while running it

I think he just wants you guys to argue. I agree with the fact that he's still gonna have a GAS MOTOR. Go ahead and go argue with those other guys OP. You'll probably hear what you heard here.

 

[Silvertip]

Re: Charging a trolling motor while running it

Both Silvertip and the OP seem to be mixing apples with oranges. The OP is mixing AC and DC amps and Silvertip is mixing 12 output with 36 volt output. If you convert input and output to power/watts it will be easier to understand. The TM output at max thrust is 46 amps at 36 volts or 1656 watts. The charger input at max amps is 15 amps at 12 volts or 180 watts. The input would be less than 1/10 of the output. Even at 15 amps per bank input, the input would be less than 1/3 the output.

As I stated in an earlier post, understanding how the charger works is as critical as knowing the input versus output if you are going to charge while using the TM. If you charger is like mine and tests the battery when first plugged in and then shuts down for 24 hours if they are 100%, you could run the generator all day and may never put anything back into the system.

I am not mixing 12/36 values. I am simply stating that the 5x3 charger will not keep up with the demand of the troller. I've owned lots of smart chargers and none of them ever shut down for 24 hours after being plugged in when the batteries are topped off. They simply go to "float" mode and return to charging if and when needed. The fact remains that the generator has no bearing whatsoever on whether it can keep up with the demand (to a point). The charger determines what the load on that generator will be so using the OP's charger, even a small 1000 watt generator would work since the demand from the charger is less than that. Yes -- the motor is sucking 46 amps but the charger output is nowhere near capable of that number. The long and short of this is that the charger determines what the load on the generator will be -- not the motor. The motor determines what the load will be on the batteries. (By the way -- I'm still waiting for someone to make a correction in my previous post.)

 

[rebocc]

Re: Charging a trolling motor while running it

It seems like the onboard charger will be your limiting factor. At max thrust, your TM will be pulling ~45 amps from each battery. If your onboard charger is supplying 5 amps per bank, you have a deficit of 40 amps. Even at its lowest setting, your TM will probably be pulling some amps from the batteries even if the generator is running. To make use of the power the generator can supply, you would have to upgrade your onboard charger.

Btw, I did more research on the 3 bank 5/5/5 battery charger, and DW is correct. Even if it's connected to a generator that produces say 1800 watts, the charger will only be able to send about 65 to 70 watts to each battery during bulk charge. 200 watts of charging power would not keep up with the trolling motor on the water. However, it would be ok for evening charging at the campsite, which is probably what I'll do for now.

For anyone who's actually interested in this idea (electric boat power), here's another interesting link i found from Fischer Panda generators - they also do electric propulsion systems.

http://www.fischerpanda.co.uk/whisperprop_10kw_48v_system.html

 

[dwparker99]

Re: Charging a trolling motor while running it

Not trying to start an argument or prove anybody wrong. Just trying to get the OP accurate info so he can choose to continue his project or abandon it.

(By the way -- I'm still waiting for someone to make a correction in my previous post.)

The maximum output of the charger, regardless what you power it with, is 15 amps so you are losing ground at 46 amps with no chargers, or 31 amps with the charger. So the practical way to look at this is that at full speed the generator can only "prolong" run time by less than 1/3 since the batteries do not charge on a linear curve.

I am not mixing 12/36 values.

You are mixing 12/36 values. You are taking 46 amps out at 36 volts and putting back in 15 amps at 12 volts. You are losing ground at 41 amps not 31. Each battery is putting out 46 amps and each is getting 5. The "prolong" run time is much less than 1/3, it is less than 1/10.

I've owned lots of smart chargers and none of them ever shut down for 24 hours after being plugged in when the batteries are topped off. They simply go to "float" mode and return to charging if and when needed.

The "float" mode is different for each manufacturer. The ones you are use to use the traditional algorithm which charges to 100%, shuts down and monitors terminal voltage until it drops through a floor say 12.8 volts and then kicks back on and charges until the voltage reaches a predetermined level say 13.6 volts and shuts back off and then continuously repeats this cycle. My Noco Gen 3 is different. According to their website, the Gen 3's "float" mode is this: "Step 8: 24 Hour Shuts off, but constantly monitors your battery by providing a gentle charge every 24 hours for maximum battery life." This is consistent with what I've experienced. I can run the trim motor and even start the big motor while the charger is hooked up and it never comes out of the charged green light mode.

Even a charger with a traditional "float" mode, if the OP is charging with the generator and the charger switches from the "bulk" mode at 5 amps to the "absorption" or "float" mode at 1-1.5 amps, I don't think the charger would drop back down into the bulk mode at 5 amps just because he started using the TM again. He would have to inquire to the manufacturer to make sure. If not, he would have to unplug the charger and plug it back in to get it back to the "bulk" charging mode at 5 amps.

 

[rebocc]

Re: Charging a trolling motor while running it

Even a charger with a traditional "float" mode, if the OP is charging with the generator and the charger switches from the "bulk" mode at 5 amps to the "absorption" or "float" mode at 1-1.5 amps, I don't think the charger would drop back down into the bulk mode at 5 amps just because he started using the TM again. He would have to inquire to the manufacturer to make sure. If not, he would have to unplug the charger and plug it back in to get it back to the "bulk" charging mode at 5 amps.

This is another good and practical point.

It would probably be most efficient to run the charger only when the battery bank goes below 75% (or something like that) to ensure you're getting a bulk charge, and not wasting your power.

 

[Silvertip]

Re: Charging a trolling motor while running it

Give dwparker a prize for the correctly identifying the consumption vs replacement number. I was beginning to wonder if anyone as paying attention. I sure hope the OP is coming to grips with this but I guess if he is still convinced this is a workable solution our work here is done (at least mine is).

 

[MH Hawker]

Re: Charging a trolling motor while running it

I noticed it but their was enough comments. my thought on the subject would be to go to a motor driven DC generator and supply the electric motor directly while runing.

 

[rebocc]

Re: Charging a trolling motor while running it

I noticed it but their was enough comments. my thought on the subject would be to go to a motor driven DC generator and supply the electric motor directly while runing.

This is also a great suggestion, since the bottleneck is the onboard charger. Thanks!

 

[duke33]

Re: Charging a trolling motor while running it

Ah, and the advice you would give is???

Get a small gas outboard.